This invention relates to a fabrication method for a semiconductor device comprising a plurality of MOS field-effect transistors connected in series. In one aspect of the invention, the device comprises a single channel crossed by plural gate electrodes, alternating between first gate electrodes and second gate electrodes, the first gate electrodes being formed prior to the second gate electrodes in the fabrication process. In another aspect of the invention, the channel is subdivided by source and drain diffusion regions between each pair of gate electrodes.
In prior-art fabrication methods of this type, the first gate electrodes are formed by a first photolithography step and covered with an insulating layer, then the second gate electrodes are formed in the space or spaces between the first gate electrodes by a second photolithography step. To allow a margin for mask alignment error between the two photolithography steps, the second gate electrodes must overlap the first gate electrodes to some extent.
This overlap, however, wastes space and imposes a certain minimum length on the first gate electrodes, which is an impediment to the achievement of high integration densities.